The present invention relates to a binder for sand for sand casting molds and to resin-coated grains of sand. More particularly, the present invention relates to a binder for molds used in casting carried out at a relatively low temperature to form aluminum castings, etc., among other things, core molds, and resin-coated grains of sand.
In the production of castings having empty spaces of complicated shapes or undercuts, in the prior art there have been used cores which can be disintegrated or dissolved after the casting and the cores are removed by disintegration or dissolution thereof after the casting. In the production of such molds, sand coated with a thermosetting resin such as phenol-formaldehyde resin is generally used. However, in case the casting temperature is low as in the casting of an aluminum alloy, the integratability is insufficient. On the other hand, the use of a core soluble in water necessitates a measure to counter environmental pollution due to the waste water.
Under the circumstances as described above, coated grains of sand having strength and capacities equivalent to those of conventional coated grains of sand and excellent disintegrating properties have been demanded for casting a core used for low temperature casting.
After intensive investigations, the inventors have found that grains of sand coated with a binder comprising cellulose acetate and a specific thermosetting resin precondensate have excellent properties for the preparation of cores for low-temperature casting. The present invention has been attained on the basis of this finding.